The present invention relates to a heating or air-conditioning system for a passenger cell of a motor vehicle including a heat exchanger through which a heating medium flows and an air stream passes. A supplementary electric heater is arranged downstream of the heat exchanger, and the same air stream passes through the supplementary electric heater. An air box holds the heat exchanger and the supplementary electric heater and serves to guide the air stream, and an electronic control unit controls the heating or air conditioning operation.
In motor vehicles with an internal combustion engine or motor which is designed to have optimized consumption, a significantly lower amount of waste heat is produced. As a result of this, the heat energy made available for heating the passenger cell by cooling the engine becomes too small. This is remedied by providing a supplementary electric heater which, when necessary, heats the air stream flowing through the heat exchanger to a higher temperature.
A heating system of the type mentioned above is known from German publication DE 37 15 194 A1. In this known heating system, the heat exchanger through which cooling water flows is arranged in a duct which carries external air to the passenger cell. In addition, a supplementary electric heater, which ensures that the air is heated during the warming-up phase of the internal combustion engine, is also provided in the duct which carries the external air. In order to heat the air as intensively as possible using the supplementary heater, the latter has a heating conductor with a large area can be regulated to a low temperature of less than 150.degree. C. The supplementary heater is formed so as to have a flat construction in the form of a box which is arranged directly downstream of the heat exchanger in the direction of flow of the air, and is mounted on the heat exchanger. The heat exchanger forms a carrier for the supplementary electric heater.
Another heating system of the type mentioned above is known from German publication DE 42 38 364 A1. In this system, the supplementary electric heater is also arranged downstream of the heat exchanger. As a result, the air stream generated by a blower initially flows through the heat exchanger, is only partially heated, and subsequently flows through the supplementary electric heater and is heated to a higher temperature. The air which is preheated in this way flows into the passenger cell. A passenger-compartment temperature sensor, which is arranged in the passenger cell and which, together with a set-point-value transmitter, determines the heating requirement and is arranged in the air stream flowing into the passenger cell, controls the flow of cooling water through the heat exchanger and the activation period of the supplementary heater using a control unit.
In yet another heating system for motor vehicles which is known from German publication DE 44 33 814 A1, a supplementary electric heater which is present is composed of a multiplicity of so-called PTC (Positive Temperature Coefficient) elements which are heated electrically and through which and around which the air stream which leaves the heat exchanger flows.
The present invention has as an object the provision of a heating or air-conditioning system of the type mentioned above which can be installed in passenger cars, of the compact class, in a way which is extremely economical in terms of installation space, and which is easy to mount.
This object is achieved by arranging the control unit downstream of the heat exchanger and the supplementary electric heater in a floor area of the air box, and by arranging the supplementary electric heater at substantially a right angle with respect to the floor area and so that, on its underside, it makes contact with the control unit.
The heating or air-conditioning system according to the invention has the advantage that the control unit is accommodated in the heating or air-conditioning box in a space-saving fashion. The heating or air-conditioning box can be integrated into the vehicle as a complete functional structural unit; all that is necessary is to connect it to the cooling water circuit of the internal combustion engine of the vehicle. By accommodating the control unit in the floor area, the air-passage cross section in the air-conditioning or heating box is adversely affected only to a slight degree.
Preferred embodiments of the heating or air-conditioning system according to the invention, with advantageous developments and improvements, are claimed.
According to one preferred embodiment of the invention, the control unit is integrated into a flat housing which is fitted on its upper side with electric contact sockets into which electric contact pins which protrude from the underside of the supplementary electric heater can be plugged. The flat housing is mounted here on the floor of the heating or air-conditioning box or forms at least part of the floor of the box. It is also possible to form at least one air outlet duct in the flat housing in order to optimize the compact design of the heating or air-conditioning box.
The invention is described in more detail below with reference to an embodiment illustrated in the drawings, each of the drawing figures providing a schematic representation.